Csi feedback and receiving methods, apparatus, device, and storage medium

ABSTRACT

Provided are CSI feedback and receiving methods, apparatuses, a device, and a storage medium. The method includes: a terminal determines PMI, the PMI includes at least one of: first base vector information, second base vector information, second coefficient amplitude information or phase information; for one transmission layer, a frequency domain resource in one preset frequency domain unit corresponds to one precoding vector, the precoding vector is a linear combination of first base vectors, and weighting coefficients used in the linear combination of the first base vectors are first coefficients; on multiple frequency domain units contained in a CSI feedback band, a vector composed of first coefficients corresponding to a same first base vector is a linear combination of second base vectors, and weighting coefficients used in the linear combination of the second base vectors are second coefficients; and the terminal feeds back CSI containing the PMI to a base station.

The present application claims priority to Chinese Patent ApplicationNo. 201811302880.2 filed on Nov. 2, 2018 to the CNIPA, the disclosure ofwhich is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to, but is not limited to, the field ofcommunications and, in particular, relates to, but is not limited to,channel state information (CSI) feedback and receiving methods, anapparatus, a device, and a storage medium.

BACKGROUND

In a multiple input multiple output (MIMO) wireless communicationsystem, precoding or beamforming is performed on multiple transmitantennas, thereby achieving the purpose of improving transmissionefficiency and reliability. In order to implement high-performanceprecoding or beamforming, a precoding matrix or a beamforming vectorneeds to be well matched with a channel, which requires that thetransmit end can smoothly obtain channel state information (CSI).Therefore, CSI feedback is a key technology for implementinghigh-performance precoding or beamforming in the MIMO system.

However, in the related art, when the CSI feedback is performed, linearweighted merging is performed on a discrete Fourier transform (DFT)vector or a Kronecker product of DFT vectors, and the vector subjectedto the weighted merging is called a codebook base vector. Informationrelated to the codebook base vector, an amplitude of a weightingcoefficient, and phase information are fed back to a base station asprecoding indication information. In order to improve the performance ofthe codebook, a terminal needs to feed back phase and/or amplitudeinformation of the weighting coefficient of each codebook base vectorfor each sub-band. Therefore, when there are a lot of sub-bands, thequantization feedback on a channel matrix may bring a large CSI feedbackoverhead, but if only information about the amplitude or the phase ofthe weighting coefficients over the entire wideband is fed back, thehigh performance gain brought by this kind of codebook feedback cannotbe fully exerted.

SUMMARY

CSI feedback and receiving methods, an apparatus, a device, and astorage medium provided by embodiments of the present disclosure can atleast solve the problem in the related art that the CSI feedbackoverhead is large when the CSI is accurately fed back.

The embodiments of the present disclosure provide a CSI feedback method.The method includes steps described below.

A terminal determines precoding matrix indication information (PMI). ThePMI includes first base vector information, second base vectorinformation and second coefficient information, and the secondcoefficient information includes second coefficient amplitudeinformation and/or second coefficient phase information. Precodingvectors corresponding to frequency domain resources in a presetfrequency domain unit are the same, a precoding vector is a linearcombination of first base vectors, and weighting coefficients used inthe linear combination of the first base vectors are first coefficients.On multiple frequency domain units contained in a CSI feedback band, avector composed of first coefficients corresponding to a same first basevector is a linear combination of second base vectors, and weightingcoefficients used in the linear combination of the second base vectorsare second coefficients.

The terminal feeds back CSI containing the PMI to a base station.

The embodiments of the present disclosure further provide a CSIreceiving method. The method includes steps described below.

A base station receives CSI containing PMI and fed back by a terminal.

The base station acquires first base vector information, second basevector information and second coefficient information from the PMI. Thesecond coefficient information includes second coefficient amplitudeinformation and/or second coefficient phase information. Precodingvectors corresponding to frequency domain resources in a presetfrequency domain unit are the same, a precoding vector is a linearcombination of first base vectors, and weighting coefficients used inthe linear combination of the first base vectors are first coefficients.On multiple frequency domain units contained in a CSI feedback band, avector composed of first coefficients corresponding to a same first basevector is a linear combination of second base vectors, and weightingcoefficients used in the linear combination of the second base vectorsare second coefficients.

The embodiments of the present disclosure further provide a CSI feedbackapparatus. The apparatus includes a determination module and a feedbackmodule.

The determination module is configured to determine precoding matrixindication information (PMI). The PMI includes first base vectorinformation, second base vector information and second coefficientinformation, and the second coefficient information includes secondcoefficient amplitude information and/or second coefficient phaseinformation. Precoding vectors corresponding to frequency domainresources in a preset frequency domain unit are the same, a precodingvector is a linear combination of first base vectors, and weightingcoefficients used in the linear combination of the first base vectorsare first coefficients. On multiple frequency domain units contained ina CSI feedback band, a vector composed of first coefficientscorresponding to a same first base vector is a linear combination ofsecond base vectors, and weighting coefficients used in the linearcombination of the second base vectors are second coefficients.

The feedback module is configured to feedback CSI containing the PMI toa base station.

The embodiments of the present disclosure further provide a CSIreceiving apparatus. The apparatus includes a receiving module and anacquisition module.

The receiving module is configured to receive CSI containing PMI and fedback by a terminal.

The acquisition module is configured to acquire first base vectorinformation, second base vector information and second coefficientinformation from the PMI. The second coefficient information includessecond coefficient amplitude information and/or second coefficient phaseinformation. Precoding vectors corresponding to frequency domainresources in a preset frequency domain unit are the same, a precodingvector is a linear combination of first base vectors, and weightingcoefficients used in the linear combination of the first base vectorsare first coefficients. On multiple frequency domain units contained ina CSI feedback band, a vector composed of first coefficientscorresponding to a same first base vector is a linear combination ofsecond base vectors, and weighting coefficients used for the linearcombination of the second base vectors are second coefficients.

The embodiments of the present disclosure further provide a terminal.The terminal includes a first processor, a first memory and a firstcommunication bus.

The first communication bus is configured to implement a connectioncommunication between the first processor and the first memory.

The first processor is configured to execute one or more programs storedin the first memory to perform the CSI feedback method described above.

The embodiments of the present disclosure further provide a basestation. The base station includes a second processor, a second memoryand a second communication bus.

The second communication bus is configured to implement a connectioncommunication between the second processor and the second memory.

The second processor is configured to execute one or more programsstored in the second memory to perform the CSI receiving methoddescribed above.

The embodiments of the present disclosure further provide acomputer-readable storage medium, which is configured to store one ormore programs executable by one or more processors to implement any oneof methods described above.

According to the CSI feedback and receiving methods, apparatuses, adevice, and a storage medium provided by embodiments of the presentdisclosure, the terminal determines the precoding matrix indicationinformation (PMI), the PMI includes the first base vector information,the second base vector information and the second coefficientinformation, and the second coefficient information includes secondcoefficient amplitude information and/or second coefficient phaseinformation; precoding vectors corresponding to frequency domainresources in a preset frequency domain unit are the same, a precodingvector is a linear combination of first base vectors, and weightingcoefficients used in the linear combination of the first base vectorsare first coefficients; on multiple frequency domain units contained aCSI feedback band, a vector composed of first coefficients correspondingto a same first base vector is a linear combination of second basevectors, and weighting coefficients used in the linear combination ofthe second base vectors are second coefficients; and the terminal feedsback the CSI containing the PMI to the base station. The CSI feedback isperformed after frequency domain and spatial domain channel coefficientsare compressed, thereby enduring the high CSI feedback performance whilereducing the CSI feedback overhead.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart of a CSI feedback method applied on a terminalside according to an embodiment one of the present disclosure;

FIG. 2 is a flowchart of a CSI receiving method applied on a basestation side according to an embodiment two of the present disclosure;

FIG. 3 is a schematic diagram of intercepting second base vectors from abandwidth part (BWP) according to an embodiment three of the presentdisclosure;

FIG. 4 is a schematic diagram of RB set division according to anembodiment four of the present disclosure;

FIG. 5 is a schematic diagram of another RB set division according tothe embodiment four of the present disclosure;

FIG. 6 is a schematic diagram of still another RB set division accordingto the embodiment four of the present disclosure;

FIG. 7 is a schematic diagram of intercepting second base vectors from aBWP according to the embodiment four of the present disclosure;

FIG. 8 is a structural diagram of a CSI feedback apparatus applied to aterminal according to an embodiment five of the present disclosure;

FIG. 9 is a structural diagram of a CSI receiving apparatus applied to abase station according to the embodiment five of the present disclosure;

FIG. 10 is a structural diagram of a terminal according to an embodimentsix of the present disclosure; and

FIG. 11 is a structural diagram of a base station according to theembodiment six of the present disclosure.

DETAILED DESCRIPTION

In a high-precision CSI feedback method in the related art, a terminalfeeds back a number of columns of a precoding matrix, i.e., a channelrank indicator (RI). A precoding vector of each layer is represented asa linear combination of a set of codebook base vectors, and the set ofcodebook base vectors may be referred to as first base vectors. Theterminal calculates weighting coefficients used in the linearcombination according to the first base vectors, and quantizes and feedsback amplitude information and phase information of the weightingcoefficients, and the weighting coefficients may be referred to as firstcoefficients. In order to improve feedback performance, the amplitudeinformation and phase information of the first coefficients usually needto be reported according to a sub-band. The sub-band is a frequencydomain granularity. For all resource blocks (RBs) contained in the CSIfeedback band, M consecutive RBs form a sub-band. In this way, the CSIfeedback band may contain N sub-bands having a size of M.

For the above CSI feedback method, on an nth sub-band fed back by theterminal, a precoding vector of a certain layer may be expressed asfollows:

f _(n) =W ₁ c _(n)

W₁ is a first base vector, for example, consists of a set of orthogonalDFT vectors or a Kronecker product of DFT vectors, and c_(n) is a vectorcomposed of the first coefficients. In general, the information in W₁ isfed back by a wideband, that is, for different sub-bands over the entireCSI feedback band, the information in W₁ is the same. Specifically, thenumber of base vectors contained in W₁ is L, that is, the number ofcolumns of W₁ is L. For example, W₁ is a block diagonal matrix, andvectors contained in the diagonal block are orthogonal DFT vectors orthe Kronecker products of DFT vectors. For a precoding vector of thislayer, first coefficients on each sub-band are combined into a followingmatrix:

$C = \begin{bmatrix}c_{11} & \cdots & c_{1N} \\\vdots & \ddots & \vdots \\c_{L\; 1} & \cdots & c_{LN}\end{bmatrix}$

When the amplitude information and phase information of elements in thematrix C are directly quantified and fed back, the feedback overheadwill be relatively large. Therefore, a CSI feedback method is neededurgently to reduce the CSI feedback overhead and ensure the high CSIfeedback performance.

To illustrate the objects, solutions and advantages of the presentapplication clearer, the embodiments of the present disclosure will bedescribed below in detail in conjunction with the embodiments anddrawings. It is to be understood that the embodiments described hereinare merely intended to explain the present application and not to limitthe present application.

Embodiment One

In order to resolve the problem in the related art that the CSI feedbackoverhead is large when the CSI is accurately fed back, this embodimentprovides a CSI feedback method. The CSI feedback method provided by thisembodiment is applied on a terminal side, as shown in FIG. 1, the methodincludes steps described below.

In S101, a terminal determines precoding matrix indication information(PMI), the PMI includes first base vector information, second basevector information and second coefficient information, and the secondcoefficient information includes second coefficient amplitudeinformation and/or second coefficient phase information; precodingvectors corresponding to frequency domain resources in a presetfrequency domain unit are the same, a precoding vector is a linearcombination of first base vectors, and weighting coefficients used inthe linear combination of the first base vectors are first coefficients;on multiple frequency domain units contained in a CSI feedback band, avector composed of first coefficients corresponding to a same first basevector is a linear combination of second base vectors, and weightingcoefficients used in the linear combination of the second base vectorsare second coefficients.

A precoding vector of each layer is represented as a linear combinationof a set of codebook base vectors, and the set of codebook base vectorsmay be referred to as first base vectors. The terminal calculatesweighting coefficients used in the linear combination according to thefirst base vectors, these weighting coefficient are first coefficients.For the precoding vector of this layer, the first coefficients in eachfrequency domain unit may form a matrix C, a transpose of each rowvector in the matrix C or each column vector of a conjugate transposematrix of the matrix C is written as a linear combination of a group ofbase vectors. The base vectors subjected to the linear combination aresecond base vectors, and weighting coefficient used when these secondbase vectors are subjected to the linear combination are secondcoefficients.

In an embodiment, the frequency domain unit includes at least one of: asub-band, a resource block (RB) or a first RB set, and a number of RBscontained in the first RB set is less than a number of RBs contained ina sub-band of the CSI feedback band.

In a practical application, different frequency domain units may beselected to achieve compression feedback effects in different levels.The CSI feedback band may include multiple sub-bands, each sub-band iscomposed of several RBs, and RBs in each sub-band may be divided intodifferent RB sets.

In some implementations of this embodiment, a second base vector is aDFT vector. It should be understood that in other implementations, thesecond base vector may also be a variation of the DFT vector, such as aKronecker product of multiple DFT vectors, a cascade form of DFTvectors, or a phase adjustment form of the cascaded DFT vector.

In some implementations of this embodiment, a dimension of a second basevector is equal to a number of frequency domain units contained in theCSI feedback band.

In some implementations of this embodiment, when the frequency domainunit is the RB, all RBs contained in the CSI feedback band are dividedinto several second RB sets.

In a practical application, when the RB is used as the frequency domainunit to perform the compress and feedback, and the number of RBscontained in the CSI feedback band is relatively large, the dimension ofthe second base vector may be large. Therefore, the second base vectoris selected in the space of a relatively large dimension, such that thedecrease of correlation will result in a decrease of the feedbackaccuracy. Based on this, in this embodiment, the feedback is compressedafter all RBs contained in the CSI feedback band are divided into RBsets.

In S102, the terminal feeds back CSI containing the PMI to a basestation.

In this embodiment, the terminal feeds back the CSI to the base station,and the base station adjusts a radio signal that needs to be sent to theterminal according to the CSI, so as to achieve a better receivingeffect on the terminal side. In a process of CSI feedback, the terminalreceives a downlink signal, and this downlink signal carries a pilot.The terminal determines channel information according to the pilotcontained in the received downlink signal, and this channel informationmay be represented as a channel matrix. The terminal selects a precodingmatrix, which best matches with the current channel condition, from acodebook according to the determined channel information, and feeds backPMI corresponding to this precoding matrix to the base station throughan uplink channel by means of a feedback link. The base station maydetermine the precoding matrix that should be used by the terminalaccording to the received PMI. It should be understood that, in additionto the PMI, the CSI fed back by the terminal may further contain acorresponding reported RI and a channel quality indicator (CQI), so thatthe base station determines a number of codewords, a number of layersand a modulation and coding scheme used by each codeword in the downlinktransmission.

In an embodiment, the step in which the terminal feeds back the CSIcontaining the PMI to the base station includes a following step: theterminal feeds back second base vector information and secondcoefficient information corresponding to each second RB set to the basestation; or, the terminal feeds back second coefficient informationcorresponding to each second RB set and second base vector informationwhich is common to all second RB sets to the base station.

In some implementations of this embodiment, the terminal may feedbackthe corresponding second base vector information and second coefficientinformation for each second RB set respectively. In otherimplementations of this embodiment, the terminal may also feedback thecorresponding second coefficient information for each second RB setrespectively, and feedback same second base vector information for allRB sets contained in the CSI feedback band.

In an embodiment, a first coefficient on a second RB set is obtainedbased on a second coefficient and a second base vector corresponding tothis second RB set.

In some implementations of this embodiment, a weighting coefficient ofan lth first base vector on each of all RBs contained in a second RB setforms a vector cl, this vector cl is a linear combination of second basevectors corresponding to this second RB set, and weighting coefficientsused in the linear combination are second coefficients corresponding tothis second RB set.

In an embodiment, a dimension of a second base vector on a second RB setis equal to a number of RBs contained in this second RB set.

In an embodiment, each second RB set in the CSI feedback band has a samenumber of contained RBs.

In an embodiment, the second RB set satisfies at least one of: RBs in asecond RB set are several consecutive RBs in the CSI feedback band; RBsin a second RB set are several RBs, which are distributed with a presetnumber of spacings, in the CSI feedback band; or, RBs in the second RBset are several RBs, which are distributed with the preset number ofspacings, on a BWP where this second RB set is located.

In some implementations of this embodiment, each second RB set mayinclude G consecutive RBs in the CSI feedback band. In otherimplementations, RBs contained in each second RB set may also becomb-like distributed RBs contained in the CSI feedback band. In stillother implementations, RBs contained in each second RB set may also becomb-like distributed RBs in the bandwidth part (BWP).

In an embodiment, a number of second RB sets which are divided by theCSI feedback band is determined based on a total number of RBs containedin the CSI feedback band.

As an implementation of this embodiment, whether the total number of RBscontained in the CSI feedback band is greater than or equal to a presetthreshold R0 is determined. If the total number of RBs contained in theCSI feedback band is greater than or equal to the preset threshold R0,the CSI feedback band is divided into M1 second RB sets. If the totalnumber of RBs contained in the CSI feedback band is less than the presetthreshold R0, the CSI feedback band is divided into M2 second RB sets.M1 and M2 are positive integers, M1 is greater than M2 and M2 is greaterthan or equal to 1.

In an embodiment, a dividing strategy used when the CSI feedback band isdivided into second RB sets is determined based on sub-band distributioninformation of sub-bands contained in the CSI feedback band.

As an implementation of this embodiment, the dividing strategy mayinclude that RBs on several consecutive sub-bands in the CSI feedbackband are divided into a same second RB set, and RBs on eachnon-consecutive sub-band are divided into different second RB sets.

In an embodiment, a number of second RB sets which are divided by theCSI feedback band is determined based on a measured channel stateinformation reference signal (CSI-RS).

In an embodiment, when the CSI includes a first portion and a secondportion, the step in which the terminal feeds back the CSI containingthe PMI to the base station include following steps: the terminalrespectively feeds back the first portion of the CSI, which contains thenumber of second RB sets, and the second portion of the CSI to the basestation. A feedback overhead of the second portion of the CSI isdetermined based on a value of the first portion of the CSI.

As an implementation of this embodiment, when CSI parameters are dividedinto the first portion and the second portion, the number M of second RBsets and parameters in the first portion of the CSI are jointly channelcoded and fed back, and the overhead of CSI parameters in the secondportion is determined by values of CSI parameters in the first portion.

In an embodiment, the method further includes following steps: whetherthe number of second RB sets which are divided by the CSI feedback bandis greater than a preset threshold is determined; if the number ofsecond RB sets which are divided by the CSI feedback band is greaterthan the preset threshold, it is determined to select K1 second basevectors; and if the number of second RB sets which are divided by theCSI feedback band is not greater than the preset threshold, it isdetermined to select K2 second base vectors; where K1 and K2 arepositive integers, and K1 is less than K2.

As an implementation of this embodiment, when the number M of the secondRB sets which are divided by the CSI feedback band is greater than M3,i.e., M>M3, the number of selected second base vectors is K1, and whenthe number M of the second RB sets which are divided by the CSI feedbackband is less than or equal to M3, i.e., M≤M3, the number of selectedsecond base vectors is K2; where K1<K2, and M3≥1.

In an embodiment, the second base vector information fed back by theterminal to the base station respectively corresponds to each piece offirst base vector information.

As an implementation of this embodiment, for a precoding vector of acertain layer, the terminal respectively reports corresponding secondbase vector information for each first base vector reported to the basestation.

In an embodiment, the second base vector information is determined in adifferential encoding manner.

As an implementation of this embodiment, the step in which the secondbase vector information is determined in the differential encodingmanner includes steps described below, second base vector informationcorresponding to lth first base vector information is obtained bydifferential encoding on second base vector information corresponding to1st first base vector information, or, by differential encoding onsecond base vector information corresponding to (l−1)th first basevector information, where l is a positive integer greater than 1.

In an embodiment, the second base vector information fed back by theterminal to the base station simultaneously corresponds to all firstbase vector information.

As an implementation of this embodiment, for a precoding vector of acertain layer, the terminal reports same second base vector informationfor all first base vectors reported to the base station.

In an embodiment, a second base vector candidate set to which the secondbase vectors belong is determined based on a parameter O, and the secondbase vector candidate set is one of {v1, . . . , vNO} or a subset of{v1, . . . , vNO}; O is a positive integer, and N is the number offrequency domain units contained in the CSI feedback band.

In this embodiment, an optional set of second base vectors is determinedaccording to O, N is a number of first frequency domain units containedin the CSI feedback band or a number of RBs contained in the second RBset, and the optional set of second base vectors is {v1, . . . , vNO} orits subset, where an Sth vector vS is:

$\begin{bmatrix}1 & {\exp\left( {j\frac{s}{NO}2\pi} \right)} & \cdots & {\exp\left( {j\frac{\left( {N - 1} \right)s}{NO}2\pi} \right)}\end{bmatrix},$

or, a transpose of this vector and/or conjugation of this vector.

In an embodiment, the manner of determining the configuration parameterO includes, but is not limited to: O is determined according to basestation configuration signaling, or, O is determined according to ameasured CSI-RS.

When CSI parameters are divided into the first portion and the secondportion, O and parameters in the first portion of the CSI are jointlychannel coded and fed back, and the overhead of CSI parameters in thesecond portion is determined by values of O and CSI parameters in thefirst portion of the CSI.

In an embodiment, when the second base vector candidate set is a subsetof {v1, . . . , vNO}, a manner of determining the second base vectorcandidate set includes at least one of: determining bits having a valueof 1 in a bit map with a length of NO configured by the base stationconfiguration signaling as the second base vector candidate set in {v1,. . . , vNO}; determining the second base vector candidate set based ona starting position of the second base vector candidate set configuredaccording to the base station configuration signaling and the number ofvectors in the second base vector candidate set; or determining a targetorthogonal vector group composing the second base vector candidate setand optional vectors in the target orthogonal vector group from severalorthogonal vector groups in {v1, . . . , vNO} according to the basestation configuration signaling; where mutually orthogonal vectorsbelong to a same orthogonal vector group.

The base station configures an optional set of second base vectors to bea subset of {v1, . . . , vNO} through signaling, and in animplementation of this embodiment, the base station configures the bitmap with the length of NO, where bits having a value of 1 representsthat a vector in {v1, . . . , vNO} corresponding to positions wherethese bits are located are optional second base vectors, and a bit witha value of 0 represents that a vector in {v1, . . . , vNO} correspondingto a position where this bit is located is a non-optional second basevector.

In another implementation of this embodiment, the base stationconfigures the starting position s_(start) of the optional set of secondbase vectors and the number s_(length) of optional sets of second basevector, and in {v₁, . . . v_(NO)}, {v_(s) _(start) _(mod NO), . . . ,v(s_(s) _(start) _(+s) _(length) _()mod NO)} is the optional base vectorcandidate set

In an embodiment, the second base vectors include mutually orthogonalvectors contained in a target orthogonal vector group selected fromseveral orthogonal vector groups in the second base vector candidateset.

In some implementations of this embodiment, {v1, . . . , vNO} is dividedinto multiple orthogonal vector groups, where mutually orthogonalvectors are divided into one group. The base station configures theoptional orthogonal vector group and optional vectors selected from theoptional orthogonal vector group through signaling. The terminal reportsan index of the selected orthogonal vector group and index informationabout K second base vectors in the corresponding orthogonal vectorgroup.

In an embodiment, the second base vectors are consecutive vectorscontained in the selected target consecutive vector group from severalconsecutive vector groups containing consecutive base vectors in thesecond base vector candidate set.

In some implementations of this embodiment, the optional set {v1, . . ., vNO} is divided into multiple vector groups, and each group contains Kconsecutive base vectors. The terminal reports an index of the selectedvector group, and K vectors contained in this group are the selectedsecond base vectors.

In some implementations of this embodiment, in multiple vector groups,an mth group is {v_((m-1)d+1 mod NO), v_((m-1)d+2 mod NO), . . . ,v_((m-1)d+K mod NO)}, where d is a positive integer less than or equalto K, and d may be determined according to base station signaling or inan agreed manner, m has a

$\left\lceil \frac{NO}{d} \right\rceil,$

value range including integers from 1 to the terminal reports the valueof m, and the selected K second base vectors are vectors contained inthe mth group.

The second vector information includes a vector group index of aselected vector group, or a vector group index of a selected vectorgroup and a vector index of a vector selected from the selected vectorgroup. When the frequency domain unit is the RB and all RBs contained inthe CSI feedback band are divided into several second RB sets, the stepin which the terminal feeds back the CSI containing the PMI to the basestation includes a following step: the terminal feeds back a same vectorgroup index to the base station for multiple second RB sets in the CSIfeedback band; or, the terminal feeds back a same vector group index tothe base station for all second RB set in the CSI feedback band, and avector index corresponding to each second RB set respectively.

In an embodiment, the second base vectors are K base vectors selectedfrom X consecutive base vectors in the second base vector candidate set;where X and K are positive integers.

In some implementations of this embodiment, the optional set {v1, . . ., vNO} is divided into multiple vector groups, and each group includes Xconsecutive base vectors. The terminal reports an index of a selectedvector group, and reports information corresponding to K second basevectors selected from this selected vector group.

The terminal reports one vector group index for all second RB setscontained in the CSI feedback band, and reports informationcorresponding to K second base vectors selected from this selectedvector group for each second RB set.

In some implementations of this embodiment, in multiple vector groups,an mth group is {v_((m-1)d+1 mod NO), v_((m-1)d+2 mod NO), . . . ,v_((m-1)d+X mod NO)}, where d is a positive integer less than or equalto X, and d may be determined according to base station signaling or inan agreed manner, m has a value range including integers from 1 to

$\left\lceil \frac{NO}{d} \right\rceil,$

and the terminal reports the value of m, and reports informationcorresponding to K second base vectors selected form the mth base vectorgroup.

In an embodiment, the second base vectors are vectors intercepted from aDFT vector with a corresponding length generated based on the number offrequency domain units contained in a downlink BWP according toconfiguration information of the CSI feedback band.

The terminal generates the DFT vector with the corresponding lengthaccording to the number of first frequency domain units contained in thedownlink BWP corresponding to the CSI, and intercepts and forms thesecond base vectors from the DFT vector according to the first frequencydomain units contained in the CSI feedback band.

In some implementations of this embodiment, if the downlink BWP containsNO frequency domain units, a DFT vector with a length of NO isgenerated, there is a one-to-one mapping between each element in the DFTvector and the NO frequency domain units, and the CSI feedback bandcontains N1 frequency domain units of the NO frequency domain units,where N1 the second base vectors intercepted from the DFT vector consistof elements mapped by the frequency domain units contained in the CSIfeedback band.

In an embodiment, when the frequency domain unit is a unit less than onesub-band, the channel quality indicator (CQI) of a sub-band contained inthe CSI is determined according to precoding vectors corresponding toall frequency domain units contained in each sub-band.

In this embodiment, when the frequency domain unit is less than onesub-band, the sub-band CQI is calculated according to precodingcorresponding to all frequency domain units contained in each sub-band.

In an embodiment, the step in which the terminal feeds back the CSIcontaining the PMI to the base station includes following steps: afterquantizing two components of the second coefficient amplitudeinformation in the PMI to be between 0 and 1, the terminal feeds backthe two quantized components to the base station; the second coefficientamplitude information is a product of the two components, and the twocomponents include a first amplitude component and a second amplitudecomponent.

In some implementations of this embodiment, the terminal feeds back acommon second amplitude component for multiple pieces of secondcoefficient amplitude information corresponding to a common first basevector, and/or, the terminal feeds back a common second amplitudecomponent for multiple pieces of second coefficient amplitudeinformation corresponding to a common second base vector.

In an embodiment, the step in which the terminal feeds back the CSIcontaining the PMI to the base station includes a following step: theterminal feeds back two components of the second coefficient phaseinformation in the PMI to the base station, and the two componentsinclude a first phase component and a second phase component.

In some implementations of this embodiment, the second phase componentis a product of the two components or a sum of the two components. Inother implementations of this embodiment, a value of the first phasecomponent in the second coefficient phase information is determinedaccording to a value of the second phase component. Furthermore, thesecond coefficient phase information may be equal to the value of thefirst phase component.

In other implementations of this embodiment, the terminal feeds back acommon second phase component for multiple pieces of second coefficientphase information corresponding to a common first base vector, and/or,the terminal feeds back a common second phase component for multiplepieces of second coefficient phase information corresponding to a commonsecond base vector.

Through the CSI feedback method provided by this embodiment, in someimplementation processes, the terminal determines the PMI, the PMIincludes the first base vector information, second base vectorinformation and second coefficient information, and the secondcoefficient information includes second coefficient amplitudeinformation and/or second coefficient phase information; precodingvectors corresponding to frequency domain resources in a presetfrequency domain unit are the same, a precoding vector is a linearcombination of first base vectors, and weighting coefficients used inthe linear combination of the first base vectors are first coefficients;on frequency domain units contained in a CSI feedback band, a vectorcomposed of the first coefficients corresponding to a same first basevector is a linear combination of second base vectors, and weightingcoefficients used in the linear combination of the second base vectorsare second coefficients; and the terminal feeds back CSI containing thePMI to a base station. The CSI feedback is performed after frequencydomain and spatial domain channel coefficients are compressed, therebyenduring the high CSI feedback performance while reducing the CSIfeedback overhead.

Embodiment Two

In order to resolve the problem in the related art that the CSI feedbackoverhead is large when the CSI is precisely fed back, this embodimentprovides a CSI receiving method. The CSI receiving method provided bythis embodiment is applied on a base station side, as shown in FIG. 2,the method includes steps described below.

In S201, a base station receives CSI containing PMI and fed back by aterminal.

In this embodiment, the base station receives the CSI sent by theterminal, and adjusts a radio signal that needs to be sent to theterminal according to this CSI, so as to achieve a better receivingeffect on the terminal side. The terminal determines channel informationaccording to a pilot contained in the received downlink signal, selectsa precoding matrix that matches with the current channel condition froma codebook, and feeds back the PMI corresponding to this precodingmatrix to the base station through an uplink channel by means of afeedback link. The base station may determine a precoding matrix used onthe terminal according to the received PMI. It should be understoodthat, in addition to the PMI, the CSI received by the base station fedback by the terminal may further include a corresponding RI and CQI, sothat the base station determines a number of codewords of the downlinktransmission, a number of layers and a modulation and coding scheme usedby each codeword.

In S202, the base station acquires first base vector information, secondbase vector information and second coefficient information from the PMI,the second coefficient information includes second coefficient amplitudeinformation and/or second coefficient phase information; precodingvectors corresponding to frequency domain resources in a presetfrequency domain unit are the same, a precoding vector is a linearcombination of first base vectors, and weighting coefficients used inthe linear combination of the first base vectors are first coefficients;on multiple frequency domain units contained in a CSI feedback band, avector composed of first coefficients corresponding to a same first basevector is a linear combination of second base vectors, and weightingcoefficients used in the linear combination of the second base vectorsare second coefficients.

A precoding vector of each layer is represented as a linear combinationof a set of codebook base vectors, and the set of codebook base vectorsmay be referred to as first base vectors. The terminal calculatesweighting coefficients used in the linear combination according to thefirst base vectors, these weighting coefficients are first coefficients.For the precoding vector of this layer, the first coefficients in eachfrequency domain unit may form a matrix C. The transpose of each rowvector in the matrix C or each column vector of a conjugate transposematrix of the matrix C is written as a linear combination of a group ofbase vectors. The base vectors subjected to the linear combination aresecond base vectors, and weighting coefficients used when the secondbase vectors are subjected to the linear combination are secondcoefficients.

In an embodiment, the frequency domain unit includes at least one of: asub-band, a resource block (RB) or a first RB set, and a number of RBscontained in the first RB set is less than a number of RBs contained ina sub-band in the CSI feedback band.

In a practical application, different frequency domain units may beselected to achieve compression feedback effects in different levels.The CSI feedback band may contain multiple sub-bands, each sub-band iscomposed of several RBs, and RBs in each sub-band may be divided intodifferent RB sets.

In some implementations of this embodiment, a second base vector is aDFT vector. It should be understood that in other implementations, thesecond base vector may also be a variation of the DFT vector, such as aKronecker product of multiple DFT vectors, a cascade form of DFTvectors, or a phase adjustment form of the cascaded DFT vector.

In some implementations of this embodiment, a dimension of the secondbase vector is equal to a number of frequency domain units contained inthe CSI feedback band.

In some implementations of this embodiment, when the frequency domainunit is the RB, all RBs contained in the CSI feedback band are dividedinto several second RB sets.

In a practical application, when the terminal performs the compress andfeedback by using the RB as the frequency domain unit, and the number ofRBs contained in the CSI feedback band is relatively large, thedimension of the second base vector may be very large. Therefore, thesecond base vector is selected from the space of a relatively largedimension, such that the decrease of correlation will result in thedecrease of the feedback accuracy. Based on this, in this embodiment,the terminal performs the compress and feedback, after all RBs containedin the CSI feedback band are divided into RB sets.

In some implementations of this embodiment, the step in which the basestation receives the CSI containing the PMI and fed back by the terminalincludes, but is not limited to, following two steps: the base stationreceives second base vector information and second coefficientinformation corresponding to each second RB set fed back by theterminal, or the base station receives second coefficient informationcorresponding to each second RB set fed back by the terminal and secondbase vector information which is common to all second RB sets.

In some implementations of this embodiment, each second RB set satisfiesat least one of: RBs in each second RB set are several consecutive RBsin the CSI feedback band; RBs in each second RB set are several RBs,which are distributed with a preset number of spacings, in the CSIfeedback band; or RBs in each second RB set are several RBs, which aredistributed with a preset number of spacings, on a BWP where this secondRB set is located.

In some implementations of this embodiment, the second base vectorinformation received by the base station and fed back by the terminalcorresponds to each first base vector information respectively, or, thesecond base vector information received by the base station and fed backby the terminal corresponds to all pieces of first base vectorinformation.

The step in which the base station receives the CSI containing the PMIand fed back by the terminal includes, but is not limited to, followingtwo steps: after the terminal quantizes two components of the secondcoefficient amplitude information to be between 0 and 1, the basestation receives the two quantized components fed back by the terminal,where the second coefficient amplitude information is a product of thetwo components, and the two components include a first amplitudecomponent and a second amplitude component; and/or, the base stationreceives the two components of the second coefficient phase informationfed back by the terminal, and the two components include a first phasecomponent and a second phase component.

Through the CSI receiving method provided by this embodiment, in someimplementation processes, the base station receives CSI containing PMIand fed back by the terminal, and the base station receives the firstbase vector information, second base vector information and secondcoefficient information from the PMI, where the second coefficientinformation includes the second coefficient amplitude information and/orsecond coefficient phase information; precoding vectors corresponding tofrequency domain resources in a preset frequency domain unit are thesame, a precoding vector is a linear combination of first base vectors,and weighting coefficients used in the linear combination of the firstbase vectors are first coefficients; on frequency domain units containedin a CSI feedback band, a vector composed of first coefficientscorresponding to a same first base vector are a linear combination ofsecond base vectors, and weighting coefficients used in the linearcombination of the second base vectors are second coefficients. Theterminal feeds back the CSI after compressing frequency domain andspatial domain channel coefficients, thereby enduring that the CSIreceived by the base station has high quantization precision whilereducing the CSI feedback overhead.

Embodiment Three

To better understand the present application, this embodiment willillustrate the CSI feedback method at the sub-band level in detail witha specific example.

A number of columns of the precoding matrix fed back by the terminal isa channel rank, i.e., RI. A precoding vector of each layer isrepresented as a linear combination of a set of codebook base vectors,and the set of codebook base vectors may be referred to as first basevectors. The terminal calculates weighting coefficients used in thelinear combination according to the first base vectors, quantizes andfeeds back amplitude information and phase information of the weightingcoefficients, and these weighting coefficients may be referred to asfirst coefficients. In order to improve the feedback performance, theamplitude information and phase information of the first coefficientsusually need to be reported according to a sub-band. The sub-band is afrequency domain granularity. For all RBs contained in the CSI feedbackband, M consecutive RBs form one sub-band. In this way, the CSI feedbackband may contain N sub-bands having a size of M.

On an nth sub-band fed back by the terminal, the precoding vector of acertain layer may be expressed as follows:

f _(n) =W ₁ c _(n)

W₁ is a first base vector, for example, consists of a set of orthogonalDFT vectors or a Kronecker product of DFT vectors, and c_(n) is a vectorcomposed of first coefficients. In general, the information in W₁ is fedback by a wideband, that is, for different sub-bands over the entire CSIfeedback band, the information in W₁ is the same. Specifically, thenumber of base vectors contained in W₁ is L, that is, the number ofcolumns of W₁ is L. For example, W₁ is a block diagonal matrix, and thevectors contained in the diagonal block are orthogonal DFT vectors orthe Kronecker products of DFT vectors. For the precoding vector of thislayer, first coefficients on each sub-band are combined into a followingmatrix C.

$C = \begin{bmatrix}c_{11} & \cdots & c_{1N} \\\vdots & \ddots & \vdots \\c_{L\; 1} & \cdots & c_{LN}\end{bmatrix}$

When the amplitude information and phase information of elements in thematrix C are directly quantified and fed back, it will bring arelatively large feedback overhead, using the compression feedbackmethod at the sub-band level according to the present solution canreduce the CSI feedback overhead while ensuring the high performance.

The transpose of each row vector in the matrix C or each column vectorof a conjugate transpose matrix of the matrix C is written as a linearcombination of a group of base vectors. For example, when the transposeof an 1^(th) row vector in the matrix C or an 1^(th) column vector ofthe conjugate transposed matrix of the matrix C is b₁, b₁ is written asa linear combination of a group of base vectors, shown as follows:

b _(l) =D _(l) a _(l)

b₁ is an N-dimensional vector, and vectors contained in D₁ are the basevectors and called the second base vectors. This group of second basevectors totally includes K vectors. a_(l) is a K-dimensional vector andincludes weighting coefficients of K second base vectors, and thesecoefficients are called the second coefficients. The terminal feeds backthe second base vector information, and the amplitude information andphase information of the second coefficients.

It should be noted that there are several factors to be taken intoconsideration in the selection of the second base vectors, i.e., thevectors in D_(l).

In some implementations of this embodiment, the second base vectors arecomposed of DFT vectors. The more specific manner for selecting thesecond base vector includes, but is not limited to, at least one offollowing manners.

In a manner A-1, for a precoding vector of a certain layer, the terminalreports corresponding second base vector information for each reportedfirst base vector.

When the second base vector is selected according to the above manner,the terminal may feedback different Dl for different l. In an optimizedexample, at least one of following manners may be further used.

In a sub-manner A-1-1, the terminal respectively and independentlyencodes and reports corresponding second base vector information foreach reported first base vector. Specifically, for each 1, the terminalindependently feeds back second base vector information contained in theDl. For example, for each 1, the terminal reports an indicationi_(l)={i₁ ⁽¹⁾, . . . , i_(l) ^((k))} for a group of second base vectors,where each parameter in il represents one second base vector. Forexample, i_(l) ^((k)) indicates a DFT vector, [1 exp (jθ_(i) _(l)_((k))) . . . exp (j(N−1)θ_(i) _(l) _((k))]^(T). In an embodiment, θ_(i)_(l) _((k)) has a value range of [0, 2π].

In a sub-manner A-1-2, for each reported first base vector, the terminalrespectively reports the corresponding second base vector informationthrough differential encoding. Specifically, the terminal feeds backsecond base vector information contained in Dl respectively for each l.For l>1, the second base vector information fed back corresponding to anlth first base vector is obtained by differential encoding on a secondbase vector corresponding to a 1st first base vector, or by differentialencoding on a second base vector corresponding to an (l−1)th first basevector. For example, for 1=1, the terminal reports an indicationi₁={i_(l) ⁽¹⁾ . . . , i_(l) ^((K))} for a group of second base vectors,where each parameter in il i₁ represents one second base vector. Forexample i_(l) ^((k)) indicates a DFT vector [1 exp(jθ_(i) _(l) _((k))) .. . exp(j(N−1)θ_(i) _(l) _((k))]^(T). For l>1, the terminal reports anindication i_(l)={il(1), . . . , i_(l) ^((K))} for the group of secondbase vectors, where i_(l) ^((k)) indicates a DFT vector [1 exp (j(θ_(i)₁ _((k))+δ_(i) _(l) _((k)))) . . . exp (N−1) (θ_(i) ₁ _((k))+δ_(i) _(l)_((k))))]^(T). In an embodiment, δ_(i) _(l) _((k)) has a value range of[0, 2π].

In some embodiments, for 1=1, the terminal reports the indicationi_(l)={i_(l) ⁽¹⁾, . . . , i_(l) ^((K))} for the group of second basevectors, where each parameter in it represents one second base vector.For example, i_(l) ^((k)) indicates a DFT vector [1 exp (jθ_(i) _(l)_((k))) . . . exp (j(N−1)θ_(i) _(l) _((k)))]^(T). For l>1, the terminalreports an indication i_(i) for the group of second base vectors, and akth second base vector is a DFT vector shown as follows:

[1 exp(j(θ_(i) ₁ _((k))+δ_(i) _(l) )) . . . exp(j(N−1)(θ_(i) ₁_((k))+δ_(i) _(l) ))]^(T)

In a manner A-2, for precoding of a certain layer, the terminal reportsa group of corresponding second base vector information for all reportedfirst base vectors, that is, all reported first base vectors use a samegroup of second base vectors. For the precoding of a certain layer, theterminal only reports indication information of the group of second basevectors, i.e., i={i₁, i₂, . . . , i_(K)}, where i_(k) represents a DFTvector shown as follows:

[1 exp(jθ _(i) _(k) ) . . . exp(j(N−1)θ_(i) _(k) )]^(T).

Each vector in D_(l)=D is a DFT vector indicated by each element in i.The final matrix C may be written as C^(T)=DA or C^(H)=DA, where A={a₁,. . . , a_(L)}.

On the other hand, the manner for determining an optional set of vectorsin D or Dl includes, but is not limited to, at least one of thefollowing manners.

In a manner B-1, the optional set of vectors is determined according tobase station configuration signaling. The more specific manner mayinclude, but is not limited to, at least one of the followingsub-manners.

In a sub-manner B-1-1, the base station configuration signalingconfigures a parameter O, and the optional set of second base vectors is{v₁, . . . , v_(NO)}, where an s^(th) vector v_(s) is

$v_{s} = {\left\lbrack {1\ {\exp\left( {j\frac{s}{NO}2} \right)}\ldots\ {\exp\left( {j\frac{\left( {N - 1} \right)s}{NO}2} \right)}} \right\rbrack^{T}.}$

In a sub-manner B-1-2, for a certain parameter O, the base stationconfigures a set of DFT vectors which may be selected as the second basevectors. For example, the base station configures a bit map with alength of NO, where a bit having a value of 1 represents that a vectorin {v₁, . . . , v_(NO)} corresponding to a position where this bithaving a value of 1 is located may be used as a candidate vector of thesecond base vectors. In another example, the base station configures astarting position sstart of an optional DFT vector and a number slengthof optional DFT vectors, then in {v₁, . . . , v_(No)}, {v_(s) _(start)_(+s) _(length) _() mod NO)}, is an optional base vector candidate set.In other embodiments, {v₁, . . . , v_(NO)} is divided into multipleorthogonal vector groups, in which mutually orthogonal vectors aredivided into one group, and the base station configures an optionalvector group and optional vectors in the selected orthogonal vectorgroup through the signaling.

In a manner B-2, the optional set of vectors is determined according toan agreed rule. For example, in the above manner B-1-1, the parameter Ohas a fixed value, for example, O=4 or O=1, or the value of theparameter O is determined according to a value of L.

In a manner B-3, the terminal determines the value of 0 according tochannel measurement. After the terminal determines the value of Oaccording to the channel measurement, the second base vector candidateset is {v₁, . . . , v_(No)}. The terminal reports the value of O, thereported O, RI, and a CQI corresponding to a first codeword are used asjoint channel coding of a first CSI portion, and the other CSIparameters are as joint channel coding of a second CSI portion, wherevalues of parameters of the first CSI portion determine the feedbackoverhead of the second CSI portion.

On the other hand, the manner for selecting second base vectors from thesecond base vector candidate set includes, but is not limited to, atleast one of following manners.

In a manner C-1, K selected second base vectors are mutually orthogonal.Specifically, the optional second base vectors are divided into multiplevector groups, and every two DFT vectors in each group are mutuallyorthogonal. For example, the optional second base vectors ar dividedinto O groups: {v_(t), v_(O+t), v_(2O+t), . . . , v_((N-1)O+t)}, where tdenotes a group index, and a value oft is {1, 2, . . . , O}. Theterminal reports a group index t selected by itself, and indexinformation of K second base vectors in the corresponding orthogonalgroup.

In a manner C-2, selected second base vectors are K consecutive secondbase vectors in the candidate set. Specifically, the candidate set {v₁,. . . , v_(NO)} is divided into multiple vector groups, and each groupcontains K consecutive second base vectors. For example, an mth group is{v_((m-1)d+1 mod NO), v_((m-1)d+2 mod NO), . . . , v_((m-1)d+K mod NO)},where d is a positive integer less than or equal to K, and d may bedetermined according to base station signaling or in an agreed manner,for example, d has an integer value obtained from dividing K by 2, and mhas a value range including integers from 1 to

$\left\lceil \frac{RO}{d} \right\rceil.$

The terminal reports the value of m, and the selected K second basevectors are the mth group of base vectors.

In a manner C-3, selected second base vectors are K base vectorsselected from X consecutive second base vector in the candidate set.Specifically, the candidate set {v₁, . . . , v_(NO)} is divided intomultiple vector groups, and each group contains X consecutive secondbase vectors. For example, an mth group is {v_((m-1)d+1 mod NO),v_((m-1)d+2 mod NO), . . . v_((m-1)d+X mod NO)} where d is a positiveinteger less than or equal to X and d may be determined according tobase station signaling or in an agreed rule, for example, d has a valueof X, or an integer value obtained from dividing K by 2, and m has avalue range including integers from 1 to

$\left\lceil \frac{NO}{d} \right\rceil.$

The terminal reports the value of m and information corresponding to Ksecond base vectors selected from the mth group of base vectors. Thevalue of X may be determined in an agreed manner or by base stationconfiguration signaling such as codebook limitation signaling.

In addition, since the CSI feedback band may contain non-consecutivesub-bands, in this case, if the full DFT vector generated by the CSIfeedback band is still used for second base vectors, the advantages ofthe DFT vector cannot be utilized, and thus second base vectors may begenerated by using a following method.

In a manner D, a DFT vector with a corresponding length is generatedaccording to the number of sub-bands contained in the downlink BWPcorresponding to the CSI, and the second base vectors are interceptedfrom this DFT vector according to the configuration of the CSI feedbackband. Specifically, as shown in FIG. 3, if the downlink BWP contains NOsub-bands, a DFT vector with a length of NO is generated, i.e., v₀={v₀⁽¹⁾, . . . , v₀ ^((NO))}^(T). There is a one-to-one mapping between eachelement in the DFT vector and the NO sub-bands. The CSI feedback bandcontains N sub-bands of the NO sub-bands, where N≤N0. The interceptedsecond base vectors consist of elements corresponding to the sub-bandscontained in the CSI feedback band.

For the quantization feedback of the second coefficient information inthe sub-band level CSI feedback method, i.e., the quantization feedbackof {a₁, . . . , a_(L)}, for precoding of a certain layer, each vectora_(l) is a K-dimensional vector including weighting coefficients for alinear combination of the second base vectors, where the linearcombination is to generate the vector consisting of weightingcoefficients of an lth first base vector in linear combinations of thefirst base vectors on N sub-bands. The second coefficients to be fedback form a following matrix.

A=[a ₁ , . . . ,a _(L)]

The feedback of the second coefficient information in the above matrix Arequires quantified feedback of amplitude information and phaseinformation of elements in the matrix. The specific manner forquantization feedback includes, but is not limited to, at least one offollowing manners.

In a manner E-1, the terminal quantifies the second coefficientamplitude information to be between 0 and 1, and feeds back thequantified second coefficient amplitude information.

In some embodiments, for the matrix A, calculated second coefficients inthe precoding of a certain layer are divided by a maximum value ofamplitude of the second coefficients, i.e.,

${A^{\prime} = {\frac{1}{M_{W}}A}},$

where m_(W) is the maximum value of amplitude of the elements in thematrix A. The terminal quantifies the amplitude of each element in theA′ to be between 0 and 1 and feeds back each quantified amplitude servedas the second coefficient amplitude information to the base station.

In a manner E-2, the terminal feeds back information of two componentsof the second coefficient amplitude. A first component of the secondcoefficient amplitude and a second component of the second coefficientamplitude are quantified to be between 0 and 1. The second coefficientamplitude used in the precoding is a product of the two components.Furthermore, for a certain first base vector, i.e., for a certain 1, twocomponents of corresponding K second coefficient amplitudes are thesame; or for a certain second base vector, i.e., for each row in thematrix A, two components of corresponding L second coefficientamplitudes are the same.

In some embodiments, for the matrix A, the matrix A′ is obtained fromdividing each element in the matrix A by the maximum value of amplitudein a row or a column where the each element is located. The amplitude ofthe element in the matrix A′ is quantified to be between 0 and 1, andthe quantized amplitude of the element served as the first component ofthe second coefficient amplitude is fed back to the base station. Inaddition, after the terminal divides the maximum value of amplitude ineach row or each column by the maximum value of the amplitude of allelements in the matrix A, the terminal quantifies the obtained values tobe between 0 and 1, and feeds back the quantified values served as thesecond component of the second coefficient amplitude to the basestation. Finally, the second coefficient amplitude used in the precodingis obtained based on a product of the corresponding first component andsecond component of the second coefficient amplitude.

For the phase quantization of the second coefficient, the performance ofthe quantization may also be improved by using a two-step quantizationmethod. The specific quantization feedback includes, but is not limitedto, at least one of following manners.

In a manner F-1, the terminal feeds back information of two componentsof the second coefficient phase. The second component represents avariation range of phase of elements in each row or each column of thematrix A, for example, the maximum value of phase, one of these secondcomponents is fed back for each row or each column, i.e., secondcoefficient phases contained in a certain row or column of the matrix Avary within a range of 0 to this maximum value of phase. Thesecalculated phases of elements in the matrix A are quantified into firstcomponents of corresponding second coefficient phases, and each firstcomponent has a value range of 0 to this maximum value of phase.Finally, a quantified second coefficient phase is equal to the firstcomponent of this second coefficient phase.

In a manner F-2, the terminal feeds back information about twocomponents of the second coefficient phase. The second componentrepresents phase variation feedback of each row or column of the matrixA, for example, the maximum value of phase, one of these secondcomponents is fed back for each row or column, i.e., second coefficientphases contained in a certain row or column of the matrix A vary withina range of 0 to this maximum value of phase. Ratios or differencesbetween phases of elements in the matrix A and the above secondcomponents are obtained according to the calculated second coefficientphases in the matrix A. These obtained ratios or differences arequantified into first components of the second coefficient phases.Finally, a quantified second coefficient phase is a product or sum ofthe first component and the second coefficient.

Embodiment Four

To better understand the present application, this embodiment willillustrate the CSI feedback method at the RB level in detail with aspecific example.

A number of columns of the precoding matrix fed back by the terminal isa channel rank, i.e., RI. A precoding vector of each layer isrepresented as a linear combination of a set of codebook base vectors,and this set of codebook base vectors may be referred to as first basevectors. The terminal calculates weighting coefficient used in thelinear combination according to the first base vectors, and quantizesand feeds back amplitude information and phase information of theweighting coefficients, and these weighting coefficients may be referredto as first coefficients. The CSI feedback band is assumed to contain RRBs. If precoding is performed at the RB level, and a linear combinationis used to represent the precoding on each RB, for a certain layer, aprecoding vector on an rth RB may be represented as follows.

f _(r) =W ₁ c _(r)

W₁ is a first base vector, for example, consists of a set of orthogonalDFT vectors or Kronecker products of DFT vectors, and c_(r) is a vectorcomposed of first coefficients. In general, the information in W₁ is fedback by a wideband, that is, for different RBs over the entire CSIfeedback band, the information in W₁ is the same. Specifically, a numberof base vectors contained in W₁ is L, that is, the number of columns ofW₁ is L. For example, W₁ is a block diagonal matrix, and vectorscontained in this diagonal block are orthogonal DFT vectors or Kroneckerproducts of DFT vectors. For a precoding vector of this layer, firstcoefficients on each RB are combined into a following matrix C.

$C = \begin{bmatrix}c_{11} & \text{...} & c_{1R} \\\vdots & \ddots & \vdots \\c_{L1} & \text{...} & c_{LR}\end{bmatrix}$

When the amplitude information and phase information of elements in thematrix C are directly quantified and fed back, it will bring arelatively large feedback overhead. On the basis of the above, in thisembodiment, a transpose of each row vector in the matrix C or eachcolumn vector in a conjugate transpose matrix of the matrix C is writtenas a linear combination of a group of base vectors. For example, whenthe transpose of an lth row vector or an lth column vector of theconjugate transposed matrix of the matrix C is b₁, b₁ is written as alinear combination of a group of base vectors, shown as follows:

b _(l) =D _(l)α_(l)

b_(l) is an R-dimensional vector, and vectors contained in D_(l) are thebase vectors and called the second base vectors. This set of second basevectors totally contains K vectors. a_(l) is a K-dimensional vector andincludes weighting coefficients of K second base vectors, and thesecoefficients are called second coefficients. The terminal feeds back thesecond base vector information, and the amplitude information and phaseinformation of the second coefficients.

In some embodiments, the base station and the terminal may determine touse a compression solution at the sub-band level or a compressionsolution at the RB level through configuration signaling and an agreedrule. The agreed rule includes a rule based on a density of anassociated CSI-RS. For example, if the density of the CSI-RS is greaterthan or equal to 1, the sub-band level compression method or theRB-level compression method may be used, but if the density of theCSI-RS is less than 1, only the sub-band level compression method may beused.

In addition, in some embodiments, when the CQI is fed back in a sub-bandmode, a CQI of a sub-band is calculated based on pre-coding of all RBscontained in this sub-band.

For the RB-level compression feedback solution, in a practicalapplication, when there may be a lot of RBs contained in the CSIfeedback band, the dimensionality of the second base vector may be verylarge. Therefore, the second base vectors are selected from the space ofa relatively large dimension, such that a decrease of correlation willresult in a decrease of the accuracy. The performance of RB-levelcompression and feedback may be further optimized by using, but are notlimited to, at least one of following manners:

In a manner A-1, RBs in the CSI feedback band are divided into M RBsets, where M>1. The terminal respectively feeds back correspondingsecond base vector information and second coefficient information foreach RB set, and the precoding on each RB set is obtained by the productof a second base vector corresponding to the each RB set and a secondcoefficient corresponding to the each RB set. The dimension of a secondbase vector on each RB set is equal to a number of RBs contained in theeach RB set.

Specifically, R RBs in the CSI feedback band are divided into M RB sets,each RB set includes G consecutive RBs, where

$G = {{\frac{R}{M}.\mspace{14mu}{If}}\mspace{14mu}\frac{R}{M}}$

is not an integer, RB sets from a 1st RB set to an (M−1)th RB set eachcontain

${\left\lceil \frac{R}{M} \right\rceil{RBs}},$

and remaining RBs belong to an Mth RB set. FIG. 4 illustrates a specificexample of diving RB sets. For the mth RB set, the precoding on a gth RBis shown as follows:

f _(m) ^((g)) =W ₁ c _(m) ^((g))

m is an integer between 1 and M, g is an integer between 1 and G. Thefirst coefficients on this RB set form a following matrix C_(m).

$C_{m} = \begin{bmatrix}{c_{m}^{(1)}(1)} & \text{...} & {c_{m}^{(G)}(1)} \\\vdots & \ddots & \vdots \\{c_{m}^{(1)}(L)} & \text{...} & {c_{m}^{(G)}(L)}\end{bmatrix}$

A transpose of an l^(th) row vector in the matrix C_(m) or an l^(th)column vector of a conjugate transposed matrix of the matrix C_(m) isb_(l) ^(m), and b_(l) ^(m) is a linear combination of a group of secondbase vectors, shown as follows:

b _(l) ^(m) =D _(l) ^(m)α_(l) ^(m)

The terminal feeds back a second base vector D_(l) ^(m) corresponding toeach RB set and the amplitude information and phase information of thesecond coefficient a_(l) ^(m).

In an embodiment, only when the number of RBs in the CSI feedback bandis greater than or equal to a threshold R0, multiple RB sets aredivided, otherwise there is only one RB set.

In an embodiment, the manner for dividing RB sets is related to thesub-bands contained in the CSI feedback band. Consecutive sub-bands inthe CSI feedback band are divided into a same RB set, andnon-consecutive sub-bands belong to different RB sets.

In an embodiment, the number M of RB sets is obtained by the terminalmeasuring the CSI-RS, and then fed back to the base station. When CSIparameters are divided into a first portion and a second portion, M andparameters in the first portion of the CSI are jointly channel coded andfed back, and the overhead of CSI parameters in the second portion isdetermined by values of M and CSI parameters in the first portion.

In an embodiment, when the number M of RB sets is greater than 1, anumber of selected second base vectors is less than the number ofselected second base vectors when the number M of RB sets is equal to 1.

In a manner A-2, RBs in the CSI feedback band are divided into M RBsets, where M>1. The terminal respectively feeds back correspondingsecond coefficient information for each RB set, and feeds back secondbase vector information for the entire band, that is, each RB set uses asame second base vector. The precoding on each RB set is obtained by aproduct of the second base vector corresponding to the each RB set andthe second coefficient corresponding to the each RB set. The dimensionof the second base vector is equal to the number of RBs contained ineach RB set. Furthermore, each RB set contains a same number of RBs. Insome embodiments, RBs contained in one RB set are distributed in acomb-like manner over the entire band, that is, RBs within a certainnumber of spacing belong to a same RB set. For example, if each RB setcontains G RBs, and the number of RBs contained in the CSI feedback bandis R, these R RBs are divided into M RB sets, and RBs with a spacing ofM RBs belong to a same RB set. The specific manner for dividing RB setsis shown in FIG. 5, where RBs are divided into two RB sets, RBs havingan even index belong to a set one and RBs having an odd index belong toa set two.

More specifically, in this manner, a vector b_(l) ^(m) formed by firstcoefficients on an mth RB set is as follows:

b _(l) ^(m) =D _(l)α_(l) ^(m)

D_(l) is same for each RB set, and may be calculated according to anyone of RB sets.

In an embodiment, only when the number of RBs in the CSI feedback bandis greater than or equal to a threshold R0, multiple RB sets aredivided, otherwise there is only one RB set.

In an embodiment the number M of RB sets is obtained by the terminalmeasuring the CSI-RS, and then fed back to the base station. When CSIparameters are divided into a first portion and a second portion, M andparameters in the first portion of the CSI are jointly channel coded andfed back, and the overhead of CSI parameters in the second portion isdetermined by values of M and parameters in the first portion of theCSI.

In an embodiment, the number of selected second base vectors with thenumber M of RB sets greater than 1 is less than the number of selectedsecond base vectors with the number M of RB sets equal to 1.

In a manner A-3, FIG. 6 illustrates a method for dividing RB sets. TheRBs in the CSI feedback band are divided into M RB sets. G consecutiveRBs belong to a same RB set, and G is less than the number of RBscontained in the sub-band. RBs in each RB set use same precoding, i.e.,RBs in each RB set use a same first coefficient. In addition, thedimension of the second base vector is equal to the number M of RB sets.Different RB sets use a same set of second base vectors and a same setof second coefficients, i.e., the terminal calculates the second basevectors and second coefficients based on first coefficients on differentRB sets.

For a certain layer, the precoding vector on an mth RB set may berepresented as follows:

f _(m) =W ₁ c _(m)

For a precoding vector of this layer, first coefficients on each RB setare combined into a following matrix C.

$C = \begin{bmatrix}c_{11} & \text{...} & c_{1M} \\\vdots & \ddots & \vdots \\c_{L1} & \text{...} & c_{LM}\end{bmatrix}$

The transpose of an l^(th) row vector in the matrix C or an l^(th)column vector of a conjugate transposed matrix of the matrix C is b₁,and b₁ is written into a linear combination of a group of base vectors,shown as follows:

b _(l) =D _(l)α_(l)

The terminal feeds back selected second base vectors in D_(l),quantifies and feeds back amplitude information and phase information ofelements in a_(l).

In an embodiment, the number G of RBs in each RB set is determined bythe number of RBs in the CSI feedback band. For example, if the numberof RBs in the CSI feedback band is greater than a certain threshold R0,then G>1, otherwise G=1.

In an embodiment, each sub-band contains M0 RB sets, and a CQI of asub-band is calculated based on the precoding on these M0 RB sets.

It should be noted that there are several factors to take intoconsideration in the selection of the second base vectors, i.e., thevectors in D_(l).

In some implementations of this embodiment, the second base vectors arecomposed of DFT vectors. The more specific manner for selecting thesecond base vectors includes, but is not limited to, at least one offollowing manners.

The number of RBs contained in the CSI band is R when the frequencydomain division methods in A-1, A-2, or A-3 is not used; the number ofRBs contained in each RB set is R when the frequency domain divisionmethods in A-1 or A-2 is used, and the number of RB sets is R when thefrequency domain division method in A-3 is used.

In a manner B-1, for a precoding vector of a certain layer, the terminalreports corresponding second base vector information for each reportedfirst base vector.

When the second base vectors are selected according to the above manner,the terminal may feedback different D₁ for different l. In an optimizedexample, at least one of following manners may be further employed.

In a sub-manner B-1-1, the terminal respectively and independentlyencodes and reports corresponding second base vector information foreach reported first base vector. Specifically, the terminalindependently feeds back second base vector information contained in theD₁ for each 1. For example, for each 1, the terminal reports anindication i_(l)={i₁ ⁽¹⁾, . . . , i_(l) ^((k))} for a group of secondbase vectors, where each parameter in it represents one second basevector. For example, i_(l) ^((k)) indicates a DFT vector [1 exp (jθ_(i)_(l) _((k))) . . . exp (j(R−1)θ_(i) _(l) _((k)))]^(T).

In a sub-manner B-1-2, the terminal respectively reports correspondingsecond base vector information through differential encoding for eachreported first base vector. Specifically, the terminal feeds back secondbase vector information contained in Dl respectively for each 1. Forl>1, the second base vector information fed back corresponding to an lthfirst base vector is obtained by differential encoding on a second basevector corresponding to a 1st first base vector, or by differentialencoding on a second base vector corresponding to an (l−1)th first basevector. For example, for l=1, the terminal reports an indicationi_(l)={i_(l) ⁽¹⁾, . . . , i_(l) ^((K))} for the group of second basevectors, where each parameter in it represents one second base vector.For example, i_(l) ^((k)) indicates a DFT vector [1 exp (jθ_(i) ₁_((k))) . . . exp (j(R−1)θ_(i) ₁ _((k)))]^(T). For l>1, the terminalreports the indication i_(l)={i_(l) ⁽¹⁾, . . . , i_(l) ^((K))} for thegroup of second base vectors, where i₁ ^((k)) indicates a DFT vector asfollows:

[1 exp(j(θ_(i) ₁ _((k))+δ_(i) ₁ _((k)))) . . . exp(j(R−1)(θ_(i) ₁_((k))+δ_(i) _(l) _((k)))]^(T)

In some embodiments, for l=1, the terminal reports the indicationi_(l)={i_(l) ⁽¹⁾, . . . , i_(l) ^((K))} for the group of second basevectors, where each parameter in i₁ represents one second base vector.For example, i_(l) ^((k)) indicates a DFT vector [1 exp (jθ_(i) _(l)_((k))) . . . exp (j(N−1)θ_(i) _(l) _((k)))]^(T). For l>1, the terminalreports the indication i₁ for the group of second base vectors, and ak^(th) second base vector is a DFT vector shown as follows:

[1 exp(j(θ_(i) ₁ _((k))+δ_(i) _(l) )) . . . exp(j(R−1)(θ_(i) ₁_((k))+δ_(i) _(l) ))]^(T)

In a manner B-2, for precoding of a certain layer, the terminal reportsa group of corresponding second base vector information for all reportedfirst base vectors, that is, all reported first base vectors use a samegroup of second base vectors. For the precoding of a certain layer, theterminal only reports indication information about the group of secondbase vectors, i.e., i={i₁, i₂, . . . , i_(K)}, where i_(k) represents aDFT vector as follows.

[1 exp(jθ _(i) _(k) ) . . . exp(j(R−1)θ_(i) _(k) )]^(T)

Each vector in D_(l)=D is a DFT vector indicated by each element in i.The final matrix C may be written as C^(T)=DA or C^(H)=DA, where A={a₁,. . . , a_(L)}.

On the other hand, the manner for determining the optional set ofvectors in D or D₁ includes, but is not limited to, at least one offollowing manners.

In a manner C-1, the optional set of vectors is determined according tobase station configuration signaling. The more specific manner mayinclude, but is not limited to, at least one of following sub-manners.It is to be noted that if the RB sets are divided by using the abovemanner A-1, the base station configures one set of signaling in at leastone of following manners for each RB sub-set.

In a sub-manner C-1-1, the base station configuration signalingconfigures a parameter O, and the optional set of second base vectors is{v₁, . . . , v_(RO)}, where an s^(th) vector v_(s) is

$v_{s} = {\left\lbrack {1\ {\exp\left( {j\frac{s}{RO}2} \right)}\ldots\ {\exp\left( {j\frac{\left( {R - 1} \right)s}{RO}2} \right)}} \right\rbrack^{T}.}$

In a sub-manner C-1-2, for a certain parameter O, the base stationconfigures a set of DFT vectors which includes vectors that may beselected as the second base vectors. For example, the base stationconfigures a bit map with a length of RO, where a bit with a value of 1represents that a vector in {v₁, . . . , v_(RO)} corresponding to aposition where this bit is located may be used as a candidate vector ofthe second base vectors. In another example, the base station configuresa starting position s_(start) of optional DFT vectors and the numbers_(length) of the optional DFT vectors, then in {v₁, . . . , v_(RO)},{v_(s) _(start) _(mod RO), . . . , v_((s) _(start) _(+s) _(length)_() mod RO)} is an optional base vector candidate set. In otherembodiments, {v₁, . . . , v_(RO)} is divided into multiple orthogonalvector groups, in which mutually orthogonal vectors are divided into onegroup, and the base station configures an optional vector group andoptional vectors in the selected orthogonal vector group according tothe signaling.

In a manner C-2, the optional set of vectors is determined according toan agreed rule. For example, in the above manner B-1-1, the value of theparameter O is fixed, for example, O=4 or O=1, or the value of theparameter O is determined according to a value of L.

In a manner C-3, the terminal determines the value of O according tochannel measurement. After the terminal determines the value of Oaccording to the channel measurement, the second base vector candidateset is {v₁, . . . , v_(RO)}. The terminal reports the value of O, thereported value of O, the RI, and a CQI corresponding to a first codewordare used as joint channel coding of a first portion of the CSI, and theother CSI parameters are as joint channel coding of a second portion ofthe CSI, where values of parameters of the first portion of the CSIdetermine the feedback overhead of the second portion.

On the other hand, the manner for selecting second base vectors from thesecond base vector candidate set includes, but is not limited to, atleast one of following manners.

In a manner D-1, K selected second base vectors are mutually orthogonal.Specifically, the optional second base vectors are divided into multiplevector groups, and every two DFT vectors in each group are mutuallyorthogonal. For example, the optional second base vectors are dividedinto O groups, {v_(t), v_(2O+t), . . . , v_((R-1)O+t)}, where t denotesa group index, and a value oft is {1, 2, . . . , O}. The terminalreports a group index t selected by itself, and index information of Ksecond base vectors in the corresponding orthogonal group.

In a manner D-2, selected second base vectors are K consecutive secondbase vectors in the candidate set. Specifically, the candidate set {v₁,. . . , v_(RO)} is divided into multiple vector groups, and each groupcontains K consecutive second base vectors. For example, an mth group is{v_((m-1)d+1 mod RO), v_((m-1)d+2 mod RO), . . . , v_((m-1)d+K mod RO)},where d is a positive integer less than or equal to K, and d may bedetermined according to base station signaling or in an agreed manner,for example, d has an integer value obtained from dividing K by 2, and mhas a value range including integers from 1 to

$\left\lceil \frac{RO}{d} \right\rceil.$

The terminal reports the value of m, and the selected K second basevectors are the mth group of base vectors.

In a manner D-3, selected second base vectors are K base vectorsselected from X consecutive second base vector in the candidate set.Specifically, the candidate set {v₁, . . . , v_(RO)} is divided intomultiple vector groups, and each group contains X consecutive secondbase vectors. For example, an mth group is {v_((m-1)d+1 mod RO),v_((m-1)d+2 mod RO), . . . , v_((m-1)d+X mod RO)}, where d is a positiveinteger less than or equal to X and d may be determined according tobase station signaling or in an agreed rule, for example, d has a valueof X, or an integer value obtained from dividing K by 2, and m has avalue range including integers from 1 to

$\left\lceil \frac{RO}{d} \right\rceil.$

The terminal reports the value of m and information corresponding to Ksecond base vectors selected from the mth group of base vectors. Thevalue of X may be determined in an agreed manner or by base stationconfiguration signaling such as codebook limitation signaling.

In some embodiments, if the RB sets are divided in the manner A-1, theterminal reports one value of m for all RB sets, that is, all RB setsuse a same m, and reports information corresponding to K second basevectors selected from the mth group of base vectors for each RB setrespectively.

In addition, since the CSI feedback band may contain non-consecutivesub-bands, in this case, if the full DFT vector generated by the CSIfeedback band is still used for the second base vectors, the advantagesof the DFT vector cannot be used, and thus the second base vectors maybe generated using the following method.

In a manner E, a DFT vector with a corresponding length is generatedaccording to the number of sub-bands contained in the downlink BWPcorresponding to the CSI, and the second base vectors are interceptedfrom this DFT vector according to the configuration of the CSI feedbackband. Specifically, as shown in FIG. 7, if the downlink BWP contains R0sub-bands, a DFT vector with a length of R0 is generated, i.e., v₀={v₀⁽¹⁾, . . . , v₀ ^((R0))}^(T). There is a one-to-one mapping between eachelement in the DFT vector and the RO sub-bands. The CSI feedback bandcontains R sub-bands of the R0 sub-bands, where R≤R0, then theintercepted second base vectors consist of elements corresponding to thesub-bands contained in the CSI feedback band

For the quantization feedback of the second coefficient information inthe sub-band level CSI feedback method, that is the quantizationfeedback of {a₁, . . . , a_(L)}, for precoding of a certain layer, eachvector a_(l) is a K-dimensional vector including weighting coefficientsfor a linear combination of the second base vectors, where the linearcombination is to generate the vector consisting of weightingcoefficients of an lth first base vector in the linear combination ofthe first base vectors on R RBs or RB sets. The second coefficients tobe fed back form the following matrix:

A=[a ₁ , . . . ,a _(L)]

The feedback of the second coefficient information in the above matrix Arequires quantified feedback of amplitude information and phaseinformation of elements in the matrix. The specific manner forquantified feedback includes, but is not limited to, at least one of thefollowing manners.

In a manner F-1, the terminal quantifies the second coefficientamplitude information to be between 0 and 1, and feeds back thequantified second coefficient amplitude information.

In some embodiments, for the matrix A, calculated second coefficients inthe precoding of a certain layer are divided by a maximum value ofamplitude of the second coefficients, i.e.,

${A^{\prime} = {\frac{1}{M_{W}}A}},$

where M_(W) is the maximum value of amplitude of the elements in thematrix A. The terminal quantifies the amplitude of each element in theA′ to be between 0 and 1 and feeds back quantified amplitudes served asthe second coefficient amplitude information to the base station.

In a manner F-2, the terminal feeds back information of two componentsof the second coefficient amplitude. A first component and a secondcomponent of the second coefficient amplitude are quantified to bebetween 0 and 1. The second coefficient amplitude used in the precodingis a product of these two components. Furthermore, for a certain firstbase vector, i.e., for a certain l, second components of corresponding Ksecond coefficient amplitudes are the same; or for a certain second basevector, i.e., for each row in the matrix A, second components ofcorresponding L second coefficient amplitudes are the same.

In some embodiments, for the matrix A, the matrix A′ is obtained throughdividing each element in the matrix A by the maximum value of amplitudein a row or column where the each element is located. The amplitude ofeach element in the matrix A′ is quantified to be between 0 and 1, andthe quantized amplitude of each element served as the first component ofthe second coefficient amplitude is fed back to the base station. Inaddition, after the terminal divides the maximum value of amplitude ineach row or each column by the maximum value of amplitude of allelements in the matrix A, the terminal quantifies the obtained values tobe between 0 and 1, and feeds back the quantified values served as thesecond component of the second coefficient amplitude to the basestation. Finally, a second coefficient amplitude used in the precodingis obtained based on a product of the first component and secondcomponent corresponding to the second coefficient amplitude.

For the quantization of the second coefficient phase, the performance ofthe quantization may also be improved by using a two-step quantizationmethod. The specific quantization feedback method includes, but is notlimited to, at least one of the following manners.

In a manner G-1, the terminal feeds back information about twocomponents of the second coefficient phase. The second componentrepresents a variation range of phase of elements in each row or columnof the matrix A, for example, the maximum value of phase, one of thesecond components is fed back for each row or column, i.e., secondcoefficient phases contained in a certain row or column of the matrix Avary from 0 to this maximum value of phase. The calculated phases ofelements in the matrix A are quantified into first components ofcorresponding second coefficient phases, where a first component has avalue range from 0 to this maximum value of phase. Finally, a quantifiedsecond coefficient phase is equal to the first component of this secondcoefficient phase.

In a manner G-2, the terminal feeds back information about twocomponents of the second coefficient phase. The second componentrepresents phase variation feedback of each row or column of the matrixA, for example, the maximum value of phase, one of the second componentsis fed back for each row or column, i.e., second coefficient phasescontained in a certain row or column of the matrix A vary from 0 to thismaximum value of phase. Ratios or a differences between phases ofelements in the matrix A and the above second components are obtainedaccording to the calculated second coefficient phases in the matrix A,and these ratios and differences are quantified into first components ofthe second coefficient phase. Finally, a quantified second coefficientphase is a product or sum of the first component and the secondcomponent of this second coefficient phase.

Embodiment Five

FIG. 8 illustrates a CSI feedback apparatus applied on a terminalaccording to an embodiment of the present disclosure. As shown in FIG.8, the apparatus includes a determination module 801 and a feedbackmodule 802.

The determination module 801 is configured to determine precoding matrixindication information (PMI), the PMI includes first base vectorinformation, second base vector information and second coefficientinformation, and the second coefficient information includes secondcoefficient amplitude information and/or second coefficient phaseinformation; for one transmission layer, precoding vectors correspondingto frequency domain resources in a preset frequency domain unit are thesame, the precoding vector is a linear combination of first basevectors, and weighting coefficients used in the linear combination ofthe first base vectors are first coefficients; on multiple frequencydomain units contained in a CSI feedback band, a vector composed offirst coefficients corresponding to a same first base vector is a linearcombination of second base vectors, and weighting coefficients used inthe linear combination of the second base vectors are secondcoefficients.

The feedback module 802 is configured to feed back CSI containing thePMI to a base station.

In this embodiment, a precoding vector of each layer is represented as alinear combination of a set of codebook base vectors, and the set ofcodebook base vectors may be referred to as first base vectors. Theterminal calculates weighting coefficients used in the linearcombination according to the first base vectors, these weightingcoefficients are first coefficients. For the precoding vector of thislayer, the first coefficient in each frequency domain unit may form amatrix C. The transpose of each row vector in the matrix C or eachcolumn vector of a conjugate transpose matrix of the matrix C is writtenas the linear combination of a group of base vectors. The base vectorsubjected to the linear combination is a second base vector, and aweighting coefficient used when the second base vector is subjected tothe linear combination is a second coefficient.

In an embodiment, the frequency domain unit includes at least one of: asub-band, a resource block (RB) or a first RB set, and a number of RBscontained in the first RB set is less than a number of RBs contained ina sub-band of the CSI feedback band.

In a practical application, different frequency domain units may beselected to achieve different levels of compression feedback effects.The CSI feedback band may include multiple sub-bands, each sub-band iscomposed of several RBs, and RBs in each sub-band may be divided intodifferent RB sets.

In some implementations of this embodiment, a second base vector is aDFT vector. It should be understood that in other implementations, thesecond base vector may also be a variation of the DFT vector, such as aKronecker product of multiple DFT vectors, a cascade form of DFTvectors, or a phase adjustment form of the cascaded DFT vector.

In some implementations of this embodiment, a dimension of a second basevector is equal to a number of frequency domain units contained in theCSI feedback band.

In some implementations of this embodiment, when the frequency domainunit is the RB, all RBs contained in the CSI feedback band are dividedinto several second RB sets.

In the practical application, when the RB is used as the frequencydomain unit to perform the compress and feedback and a number of RBscontained in the CSI feedback band is relatively large, the dimension ofthe second base vector may be very large. Therefore, the second basevector is selected in the space of a relatively large dimension, so thatthe decrease of correlation will result in a decrease of the feedbackaccuracy. Based on this, in this embodiment, the compress and feedbackis performed after all RBs contained in the CSI feedback band aredivided into RB sets.

In some implementations of this embodiment, the feedback module 802 isspecifically configured to: feedback second base vector information andsecond coefficient information corresponding to each second RB set tothe base station; or feedback, by the terminal, second coefficientinformation corresponding to each second RB set and second base vectorinformation which is common to all second RB sets to the base station.

In some implementations of this embodiment, the second RB set satisfiesat least one of: RBs in the second RB set are several consecutive RBs inthe CSI feedback band; RBs in the second RB set are several RBs, whichare distributed with the preset number of spacings, in the CSI feedbackband; or RBs in the second RB set are several RBs, which are distributedwith the preset number of spacings, on a BWP where this second RB set islocated.

In addition, when the determination module 801 performs a division ofsecond RB sets, in one implementation, the number of the second RB setsdivided from the CSI feedback band is determined based on a total numberof RBs contained in the CSI feedback band. In another implementation, adividing strategy adopted when the CSI feedback band is divided intosecond RB sets is determined based on sub-band distribution informationof sub-bands contained in the CSI feedback band. In still anotherimplementation, the number of the second RB sets divided from the CSIfeedback band is determined based on a measured channel stateinformation reference signal (CSI-RS).

It should be noted that in the practical application, the determinationmodule 801 is further configured to determine whether the number ofsecond RB sets divided from the CSI feedback band is greater than apreset threshold; if the number of second RB sets divided from the CSIfeedback band is greater than the preset threshold, the determinationmodule 801 is further configured to determine to select K1 second basevectors; and if the number of second RB sets divided from the CSIfeedback band is not greater than the preset threshold, thedetermination module 801 is further configured to determine to select K2second base vectors; where K1 and K2 are positive integers, and K1 isless than K2.

In some implementations, the second base vector information fed back bythe terminal to the base station respectively corresponds to each pieceof first base vector information. In other implementations, the secondbase vector information fed back by the terminal to the base stationsimultaneously corresponds to all first base vector information.

In some implementations, a second base vector candidate set to which thesecond base vectors belong is determined based on a parameter O, wherethe second base vector candidate set is one of {v1, . . . , VNO} or asubset of {v1, . . . , VNO}; where O is a positive integer, and N is thenumber of frequency domain units contained in the CSI feedback band. Theparameter O may be determined according to base station configurationsignaling; or, the parameter O may be determined according to a measuredCSI-RS.

It should be noted that in this embodiment, the manner for selectingsecond base vectors includes, but is not limited to, at least one of:the second base vectors are mutually orthogonal vectors contained in atarget orthogonal vector group selected from several orthogonal vectorgroups in the second base vector candidate set; the second base vectorsare consecutive vectors contained in a selected target consecutivevector group selected from several consecutive vector groups containingseveral consecutive base vectors in the second base vector candidateset; the second base vectors are K base vectors selected from Xconsecutive base vectors in the second base vector candidate set, whereX and K are positive integers; or the second base vectors are vectorsintercepted from a DFT vector with a corresponding length generatedbased on the number of frequency domain units contained in a downlinkBWP according to configuration information of the CSI feedback band.

It should further be noted that in this embodiment, the feedback module802 is further configured to, after two components of the secondcoefficient amplitude information in the PMI are quantized to be between0 and 1, feedback the two quantized components to the base station,where the second coefficient amplitude information is a product of thetwo components, and the two components include a first amplitudecomponent and a second amplitude component. In addition, the feedbackmodule 802 may further configured to feedback two components of thesecond coefficient phase information in the PMI to the base station,where the second coefficient phase information is a product of the twocomponents or a sum of the two components, and the two componentsinclude a first phase component and a second phase component.

FIG. 9 illustrates a CSI receiving apparatus applied on a base stationaccording to an embodiment of the present disclosure. As shown in FIG.9, the apparatus includes a receiving module 901 and an acquisitionmodule 902.

The receiving module 901 is configured to receive CSI containing PMI andfed back by a terminal.

The acquisition module 902 is configured to acquire first base vectorinformation, second base vector information and second coefficientinformation from the PMI, the second coefficient information includessecond coefficient amplitude information and/or second coefficient phaseinformation; precoding vectors corresponding to frequency domainresources in a preset frequency domain unit are the same, the precodingvector is a linear combination of first base vectors, and weightingcoefficients used in the linear combination of the first base vectorsare first coefficients; on multiple frequency domain units contained ina CSI feedback band, a vector composed of first coefficientscorresponding to a same first base vector is a linear combination ofsecond base vectors, and weighting coefficients used in the linearcombination of the second base vectors are second coefficients.

The receiving module 901 is further configured to receive the CSI sentby the terminal, and adjust a radio signal that needs to be sent to theterminal according to the CSI, to achieve a better receiving effect onthe terminal side. The terminal determines channel information accordingto a pilot contained in the received downlink signal, selects aprecoding matrix that matches with the current channel condition from acodebook, and feeds back PMI corresponding to this precoding matrix tothe base station through an uplink channel by means of a feedback link.The base station may determine a precoding matrix used on the terminalaccording to the received PMI. It should be understood that, in additionto the PMI, the CSI received by the receiving module 901 fed back by theterminal may further include the corresponding RI and CQI, so that thebase station determines a number of codewords in the downlinktransmission, a layer number in the downlink transmission and amodulation and coding scheme used by each codeword in the downlinktransmission.

In addition, a precoding vector of each layer is represented as a linearcombination of a set of codebook base vectors, and the set of codebookbase vectors may be referred to as first base vectors. The terminalcalculates weighting coefficients used in the linear combinationaccording to the first base vectors, these weighting coefficients arefirst coefficients. For the precoding vector of this layer, the firstcoefficients in each frequency domain unit may form a matrix C. Thetranspose of each row vector in the matrix C or each column vector of aconjugate transpose matrix of the matrix C is written as the linearcombination of a group of base vectors. The base vector subjected to thelinear combination is a second base vector, and a weighting coefficientused when the second base vector is subjected to the linear combinationis a second coefficient.

It should be understood that, the frequency domain unit includes atleast one of: a sub-band, a resource block (RB) or a first RB set, and anumber of RBs contained in the first RB set is less than a number of RBscontained in a sub-band of the CSI feedback band.

In some implementations of this embodiment, when the frequency domainunit is the RB, all RBs contained in the CSI feedback band are dividedinto several second RB sets.

In the practical application, the second RB set satisfies at least oneof characteristics: RBs in the second RB set are several consecutive RBsin the CSI feedback band; RBs in the second RB set are several RBs,which are distributed with the preset number of spacings, in the CSIfeedback band; or RBs in the second RB set are several RBs, which aredistributed with the preset number of spacings, on a BWP where thissecond RB set is located.

Through the CSI feedback apparatus provided by this embodiment, in someimplementation processes, the determination module is configured todetermine precoding matrix indication information (PMI), the PMIincludes first base vector information, second base vector informationand second coefficient information, and the second coefficientinformation includes second coefficient amplitude information and/orsecond coefficient phase information; precoding vectors corresponding tofrequency domain resources in a preset frequency domain unit are thesame, the precoding vector is a linear combination of first basevectors, and weighting coefficients used in the linear combination ofthe first base vectors are first coefficients; on frequency domain unitscontained in a CSI feedback band, a vector composed of firstcoefficients corresponding to a same first base vector is a linearcombination of second base vectors, and weighting coefficients used inthe linear combination of the second base vectors are secondcoefficients; and the feedback module is configured to feedback CSIcontaining the PMI to a base station. The terminal feeds back CSI afterfrequency domain and spatial domain channel coefficients are compressed,thereby enduring the high CSI feedback performance while reducing theCSI feedback overhead.

Embodiment Six

This embodiment further provides a terminal, and as shown in FIG. 10,the terminal includes a first processor 1001, a first memory 1002 and afirst communication bus 1003. The first communication bus 1003 isconfigured to implement a connection communication between the firstprocessor 1001 and the first memory 1002. The first processor 1001 isconfigured to execute one or more computer programs stored in the firstmemory 1002 to perform at least one step of the CSI feedback method onthe terminal side described above.

This embodiment further provides a base station, as shown in FIG. 11,the base station includes a second processor 1101, a second memory 1102and a second communication bus 1103. The second communication bus 1103is configured to implement a connection communication between the secondprocessor 1101 and the second memory 1102. The second processor 1101 isconfigured to execute one or more computer programs stored in the secondmemory 1102 to perform at least one step of the CSI receiving method onthe base station side described above.

This embodiment further provides a computer readable storage medium. Thecomputer readable storage medium includes volatile or nonvolatile,removable or non-removable media implemented in any method or technologyfor storing information (such as computer readable instructions, datastructures, computer program modules or other data). The computerreadable storage medium includes, but is not limited to, a random accessmemory (RAM), a read-only memory (ROM), an electrically erasableprogrammable read only memory (EEPROM), a flash memory, or other memorytechnologies, a compact disc read-only memory (CD-ROM), a digitalversatile disc (DVD) or another optical disc storage, a magneticcassette, a magnetic tape, disk storage or another magnetic storageapparatus, or any other medium used for storing desired information andaccessible by a computer.

The computer readable storage medium in this embodiment may beconfigured to store one or more computer programs executable by aprocessor to implement at least one step of the methods in theembodiments described above.

This embodiment further provides a computer program which may bedistributed on a computer readable medium and executed by a computingapparatus to implement at least one step of the methods in theembodiments described above. In some circumstances, the at least onestep illustrated or described may be executed in sequences differentfrom those described in the above embodiments.

This embodiment further provides a computer program product including acomputer readable apparatus on which the computer program shown above isstored. The computer readable apparatus in this embodiment may includethe computer readable storage medium shown above.

It can be seen that those of ordinary skill in the art should understandthat functional modules/units in all or part of the steps of the method,the system and the apparatus disclosed above may be implemented assoftware (which may be implemented by computer program codes executableby a computing apparatus), firmware, hardware and appropriatecombinations thereof. In the hardware implementation, the division ofthe functional modules/units mentioned above may not correspond to thedivision of physical components. For example, one physical component mayhave multiple functions, or one function or step may be performedjointly by several physical components. Some or all physical componentsmay be implemented as software executed by processors such as centralprocessing units, digital signal processors or microcontrollers,hardware, or integrated circuits such as application specific integratedcircuits.

In addition, as is known to those of ordinary skill in the art, acommunication medium generally includes computer readable instructions,data structures, computer program modules or other data in modulateddata signals such as carriers or other transmission mechanisms, and mayinclude any information delivery medium. Therefore, the presentapplication is not limited to any specific combination of hardware andsoftware.

The above content is a further detailed description of the presentdisclosure in conjunction with the specific embodiments, and thespecific implementation of the present application is not limited to thedescription. For those skilled in the art to which the presentdisclosure pertains, a number of simple deductions or substitutions maybe made without departing from the concept of the present applicationand should fall within the protection scope of the present application.

1. A channel state information (CSI) feedback method, comprising: determining, by a terminal, precoding matrix indication information (PMI), wherein: the PMI comprises: first base vector information associated with first base vectors; second base vector information associated with second base vectors; and second coefficient information, used to derive first coefficients and second coefficients, the second coefficient information comprising second coefficient amplitude information and second coefficient phase information; a CSI feedback band comprises a plurality of frequency domain units, each frequency domain unit having a plurality of frequency domain resources; frequency domain resources in each of the plurality of frequency domain units of a same transmission layer correspond to a same precoding vector, each precoding vector being a linear combination of the first base vectors with weighting coefficients being the first coefficients; and the first coefficients corresponding to a same first base vector define a first coefficient vector, the first coefficient vector being a linear combination of the second base vectors with weighting coefficients being the second coefficients; and feeding back, by the terminal, CSI containing the PMI to a base station.
 2. The method of claim 1, wherein a frequency domain unit of the plurality of frequency domain units comprises at least one of: a sub-band or a first resource block (RB) set, wherein a number of RBs contained in the first RB set is less than a number of RBs contained in a sub-band of the CSI feedback band.
 3. The method of claim 1, wherein the second base vectors comprise discrete Fourier transform (DFT) vectors.
 4. The method of claim 1, wherein a dimension of each second base vector is equal to a number of frequency domain units contained in the CSI feedback band. 5.-22. (canceled)
 23. The method of claim 1, wherein the second base vectors belong to a second base vector candidate set, the second base vector candidate set is determined based on parameter N, and the second base vector candidate set is {v₁, . . . v_(N)} or a subset of {v₁, . . . , v_(N)}, wherein N is a number of frequency domain units contained in the CSI feedback band.
 24. (canceled)
 25. The method of claim 23, wherein when the second base vector candidate set is the subset of {v₁, . . . , v_(N)}, a method of determining the second base vector candidate set comprises: determining the second base vector candidate set based on a starting position of the second base vector candidate set and a number of vectors in the second base vector candidate set. 26.-29. (canceled)
 30. The method of claim 1, wherein the second base vectors comprise K base vectors selected from X consecutive base vectors in a second base vector candidate set, and X and K are positive integers. 31.-32. (canceled)
 33. The method of claim 1, wherein the second coefficient amplitude information comprises two components to be quantized to be between 0 and 1 to generate two quantized components, wherein a coefficient amplitude used in the precoding vector is a product of the two quantized components and the two components comprise a first amplitude component and a second amplitude component.
 34. The method of claim 33, wherein feeding back, by the terminal, the CSI containing the PMI to the base station comprises at least one of: feeding back a common second amplitude component for a plurality of pieces of second coefficient amplitude information corresponding to a common first base vector; or feeding back a common second amplitude component for a plurality of pieces of second coefficient amplitude information corresponding to a common second base vector. 35.-38. (canceled)
 39. A channel state information (CSI) receiving method, comprising: receiving, by a base station, CSI containing precoding matrix indication information (PMI) from a terminal; and acquiring, by the base station, first base vector information associated with first base vectors, second base vector information associated with second base vectors, and second coefficient information from the PMI, the second coefficient information being used to derive first coefficients and second coefficients, wherein: the second coefficient information comprises second coefficient amplitude information and second coefficient phase information; a CSI feedback band comprises a plurality of frequency domain units, each frequency domain unit having a plurality of frequency domain resources; frequency domain resources in each of the plurality of frequency domain units of a same transmission layer correspond to a same precoding vector, each precoding vector being a linear combination of the first base vectors with weighting coefficients being the first coefficients; and the first coefficients corresponding to a same first base vector defines a first coefficient vector, the first coefficient vector being a linear combination of the second base vectors with weighting coefficients being the second coefficients.
 40. The method of claim 39, wherein the frequency domain unit comprises at least one of: a sub-band or a first resource block (RB) set, wherein a number of RBs contained in the first RB set is less than a number of RBs contained in a sub-band of the CSI feedback band. 41.-44. (canceled)
 45. The method of claim 39, wherein receiving, by the base station, the CSI containing the PMI from the terminal: receiving, by the base station, the CSI including two components of the second coefficient amplitude information and quantizing the two components to be between 0 and 1 to generate two quantized components, wherein a coefficient amplitude used in the precoding vector is a product of the two quantized components and the two components comprise a first amplitude component and a second amplitude component.
 46. A channel state information (CSI) feedback apparatus, applied to a terminal, comprising: at least one processor, configured to determine precoding matrix indication information (PMI), wherein: the PMI comprises first base vector information associated with first base vectors, second base vector information associated with second base vectors, and second coefficient information, used to derive first coefficients and second coefficients, the second coefficient information comprising of second coefficient amplitude information and second coefficient phase information; a CSI feedback band comprises a plurality of frequency domain units, each frequency domain unit having a plurality of frequency domain resources; frequency domain resources in each of the plurality of frequency domain units of a same transmission layer corresponds to a same precoding vector, each precoding vector being a linear combination of the first base vectors with weighting coefficients being the first coefficients; and the first coefficients corresponding to a same first base vector define a first coefficient vector, the first coefficient vector being a linear combination of the second base vectors with weighting coefficients being the second coefficients; and a transmitter in communication with a base satiation, configured to feedback CSI containing the PMI to the base station.
 47. (canceled)
 48. A base station, comprising: a memory, storing at least one program; and at least one processor in communication with the memory and configured to execute the at least one program to perform the steps, comprising: receiving CSI containing precoding matrix indication information (PMI) from a terminal; and acquiring first base vector information associated with first base vectors, second base vector information associated with second base vectors, and second coefficient information from the PMI, the second coefficient information being used to derive first coefficients and second coefficients, wherein: the second coefficient information comprises second coefficient amplitude information and second coefficient phase information; a CSI feedback band comprises a plurality of frequency domain units, each frequency domain unit having a plurality of frequency domain resources; frequency domain resources in each of the plurality of frequency domain units of a same transmission layer correspond to a same precoding vector, each precoding vector being a linear combination of the first base vectors with weighting coefficients being the first coefficients; and the first coefficients corresponding to a same first base vector define a first coefficient vector, the first coefficient vector being a linear combination of the second base vectors with weighting coefficients being the second coefficients. 49.-50. (canceled)
 51. The method of claim 23, wherein a s^(th) vector of the second base vector candidate set is $\left\{ {1\ {\exp\left( {j\frac{s}{N}2} \right)}\ldots\ {\exp\left( {j\frac{\left( {N - 1} \right)s}{N}2} \right)}} \right\},$ s being a positive integer.
 52. The CSI feedback apparatus of claim 46, wherein a frequency domain unit of the plurality of frequency domain units comprises at least one of: a sub-band; or a first resource block (RB) set, wherein a number of RBs contained in the first RB set is less than a number of RBs contained in a sub-band of the CSI feedback band.
 53. The CSI feedback apparatus of claim 46, wherein the second base vectors comprise discrete Fourier transform (DFT) vectors.
 54. The CSI feedback apparatus of claim 46, wherein a dimension of each second base vector is equal to a number of frequency domain units contained in the CSI feedback band.
 55. The CSI feedback apparatus of claim 46, wherein the second base vectors belong to a second base vector candidate set, the second base vector candidate set is determined based on a parameter N, and the second base vector candidate set is {v₁, . . . , v_(N)} or a subset of {v₁, . . . , v_(N)}, wherein N is a number of frequency domain units contained in the CSI feedback band.
 56. The CSI feedback apparatus of claim 55, wherein the at least one processor is further configured to determine the second base vector candidate set based on a starting position of the second base vector candidate set and a number of vectors in the second base vector candidate set.
 57. The CSI feedback apparatus of claim 55, wherein a s^(th) vector of the second base vector candidate set is $\left\{ {1\ {\exp\left( {j\frac{s}{N}2} \right)}\ldots\ {\exp\left( {j\frac{\left( {N - 1} \right)s}{N}2} \right)}} \right\},$ s being a positive integer.
 58. The CSI feedback apparatus of claim 46, wherein the second base vectors comprise K base vectors selected from X consecutive base vectors in a second base vector candidate set, and X and K are positive integers.
 59. The CSI feedback apparatus of claim 46, wherein the second coefficient amplitude information comprises two components to be quantized to be between 0 and 1 to generate two quantized components, wherein a coefficient amplitude used in the precoding vector is a product of the two quantized components, and the two components comprise a first amplitude component and a second amplitude component.
 60. The CSI feedback apparatus of claim 57, to feedback the CSI containing the PMI to the base station, the transmitter is configured to perform at least one of the steps comprising: feeding back a common second amplitude component for a plurality of pieces of second coefficient amplitude information corresponding to a common first base vector; or feeding back a common second amplitude component for a plurality of pieces of second coefficient amplitude information corresponding to a common second base vector. 